Connector for connecting a three-phase cable and manufacturing method of the connector

ABSTRACT

The invention relates to a connector and a manufacturing method thereof for a three-phase cable including concentric, segmentally disposed phase conductors (1) with surrounding insulation structures (11) and a concentric earth conductor (8) enclosing the phase conductors. According to the invention, the phase conductors (1) inside the connector are isolated from each other by a star-shaped dividing insulation piece (3) keeping the phase conductors (1) separate in their segments. Phase terminals (2) of the connector are disposed on the segment bottoms of the dividing insulation piece (3). The connector further incorporates a clamp (5, 7) suited for pressing the phase conductors (1) against the phase terminals (2) and a ferrule (10) on which the earth conductor (8) can be bent backward to mechanically lock a receptacle.

BACKGROUND OF THE INVENTION

The present invention relates to a connector according to the preambleof claim 1 for connecting a three-phase cable.

The invention also concerns a manufacturing method for the connector.

Connection of a three-phase squirrel-cage or synchronous motor ininverter-driven systems is most frequently performed by means of acopper or aluminium cable having three symmetrically placed phaseconductors surrounded by a common concentric earth conductor. Connectionto the drive acting as the load is conventionally performed using aterminal block at low current levels and cable lugs at higher currentlevels. The concentric earth conductor is bundled into a "tail" divertedfrom the side of the cable and then connected using either of theabove-mentioned termination methods.

Such a termination method has several shortcomings. Firstly, the jointunavoidably becomes long end bulky, because the phase conductors must bediverted apart from each other prior to the jointing. Secondly, at leastfour separate jointing steps must be carried out, three for the phaseconductors and one for the earth conductor. In the case of segmentalphase conductors, they must be dressed into a round shape beforejointing. Besides the connections, the cable must be secured by means ofa separate strain relief.

The phase and earth conductors, which are diverted apart from each otherfor the connection, form loops and radiating dipoles for the currentspassing through them thus giving rise to stray inductances and emissionof electromagnetic fields to their surroundings. To avoid suchinterference, the phase conductors should be arranged to run assymmetrically and as close to each other as possible. Furthermore, thelength of the phase conductors exposed from under the concentric earthconductor should be minimized.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the drawbacks ofthe above-described technology and to provide an entirely novelconnector for connecting a three-phase cable and a method formanufacturing such a connector.

The goal of the invention is achieved by means of providing apurpose-designed symmetrical connector for connecting a cable ininverter-driven systems, in which connector the insertion of all threephase conductors into the connector occurs in a single jointing step andthe earth connector is continued in its concentric form into theinterior of the connector housing. Simultaneously, the concentricjointing of the earth conductor acts as the strain relief for the cable.

More specifically, the connector according to the invention isprincipally characterized by what is stated in the characterizing partof claim 1.

Furthermore, the method according to the invention is principallycharacterized by what is stated in the characterizing part of claim 3.

The invention offers significant benefits.

Jointing can be made in a single step. At the same time the jointingstep provides an effective strain relief. Moreover, the embodimentaccording to the invention provides an electrical interference levelmuch lower than that of conventional constructions. Further scope ofapplicability of the present invention will become apparent from thedetailed description given hereinafter. However, it should be understoodthat the detailed description and specific examples, while indicatingpreferred embodiments of the invention, are given by way of illustrationonly, since various changes and modifications within the spirit andscope of the invention will become apparent to those skilled in the artfrom this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be examined in greater detail withreference to exemplifying embodiments illustrated in the appendeddrawings in which:

FIG. 1 is a side view of a connector according to the invention;

FIG. 2 is a cross-sectional view along the plane 2--2 of the connectorshown in FIG. 1;

FIG. 3 is a cross-sectional view along the plane 3--3 of the connectorshown in FIG. 1;

FIG. 4 is a cross-sectional view along the plane 4--4 of the connectorshown in FIG. 1;

FIG. 5 is a cross-sectional view along the plane 5--5 of the connectorshown in FIG. 1; and

FIG. 6 is a cross-sectional view along the plane 6--6 of the connectorshown in FIG. 1;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-6, the connector according to the invention and themanufacturing method thereof are now described.

In contrast to conventional jointing methods, the phase conductors 1 ofthe cable will not be diverted apart for connection under parallelterminals. Instead, they are left in their natural positions andinserted unbent into a purpose-designed connector having a concentricstructure, wherein the individual phase conductors 1 are disposed intocircularly symmetrical segments of 120°. Referring to FIG. 6, the bottomin each segment terminal of the connector is shaped into a contactterminal 2 which is suited to make electrical contact with a phaseconductor 1. In addition, the contact terminal 2 is continued as anisolated bar in the connector body and is finally connected to aninverter drive using appropriate means. The stripped lengths of thephase conductors 1 are radially compressed toward each other by means ofa clamp or clamp proper 5 resembling a conventional hose clamp so as toprovide good electrical contact between the phase conductors 1 and thesegment terminals 2. Between the clamp ring 7 and the phase conductors 1are adapted insulation pieces 4 and springed elements 6. The springedelements find use in the connection of aluminium conductor cables.Typically, the springed element 6 is a wave plate of spring steel to beplaced between the clamp ring 7 and the insulation piece 4. Theconnector is typically encased in a metallic housing acting as an EMIshield, whereby the concentric earth conductor 8 is clamped to thefeedthrough flange of the housing by means of a ferrule. The completedconnection of the cable retains full symmetry and offers the bestpossible protection against EMI.

The work stages of connector manufacture are as follows:

1. Starting from the end of the cable, the plastic sheath 9 acting asinsulation is removed over a length of approx. 50-150 mm, advantageouslyapprox. 90 mm such that the concentric multiwire copper earth conductor8 is exposed. A steel ferrule 10 is inserted onto the exposed length ofthe concentric conductor, at its very stem, onto which ferrule all theseparate copper wires of the earth conductor are bent backward. Thecopper wires are trimmed at the point where the ferrule 10 rests againstthe plastic sheath 9. This arrangement serves for strain relief anddirect connection of the earth conductor to the metallic body of theadapter-type connector.

2. Insulating plastic wrappings 11 covering the phase conductors 1 areremoved and the ends of the segment-shaped phase conductors 1 arestripped free over a length of approx. 5-50 mm, advantageously approx.20 mm. For an aluminium conductor cable, oxide is removed from the innersurfaces of the conductor in a conventional manner such as applyingcontact grease if necessary.

Outward bending of the phase conductors 1 is kept to the minimum savefor the insulation and oxide removal steps of the conductors. At thisstage, the cable end is ready for termination.

3. The exposed cable end with the segment terminals is pushed so deepinto the connector as to align the earth conductor ferrule 10 with thecenter of the feedthrough flange of the EMI shield housing.

4. The phase conductors 1 are compressed against the segment terminals 2with the help of the clamp 5 using a torque-indicating wrench todetermine the proper tightening torque.

5. Finally, the upper part of the EMI shield housing is attached inplace such that the earth conductor 8 of the cable remains compressedinside the feedthrough flange, whereby reliable electrical connectionand good strain relief are established.

In the context of the invention, the EMI shield housing can beappropriately called the receptacle of the connector. The inventionbeing thus described, it will be obvious that the same may be varied inmany ways. Such variations are not to be regarded as a departure fromthe spirit and scope of the invention, and all such modifications aswould be obvious to one skilled in the art are intended to be includedwithin the scope of the following claims.

I claim:
 1. A connector for a three-phase cable having concentric,segmentally disposed phase conductors with surrounding insulationstructures and a concentric earth conductor enclosing the phaseconductors the connector comprising: a star-shaped dividing insulationpiece for isolating the phase conductors inside the connector from eachother, said star-shaped dividing insulation piece keeping the phaseconductors separate in their segments;phase terminals disposed onsegment bottoms of said dividing insulation piece; a clamp means forpressing the phase conductors against the phase terminals; and a ferruleon which the earth conductor is bent backward for mechanically lockingthe connector to a receptacle.
 2. A connector as defined in claim 1,wherein said clamp means include a clamp ring and a clamp proper.
 3. Aconnector manufacturing method for a three-phase cable comprisingconcentric, segmentally disposed phase conductors with surroundinginsulation structures and a concentric earth conductor enclosing thephase conductors, the phase conductors being electrically connected toelectrical terminals communicating with an electrical load and an end ofthe cable is stripped of insulation material enclosing the earthconductor the method comprising the steps of:inserting a steel ferruleonto the earth conductor at a stem thereof; bending backwards separatecopper wires of the earth conductor; trimming the copper wires at apoint where the ferrule rests against a plastic sheath; removing theinsulation material covering the phase conductors; stripping the ends ofthe phase conductors; pushing an exposed end of the cable with segmentterminals deep into the connector to align the ferrule of the earthconductor with a center of a feedthrough flange of a body structure of areceptacle; pressing the phase conductors against segment terminals withclamp means; and attaching the connector to the receptacle so that theearth conductor of the cable remains pressed against the feedthroughflange, whereby reliable electrical connection and good strain reliefare established.
 4. A method as defined in claim 3, further comprisingthe step of removing the insulation of the earth conductor over a lengthof approximately 50-150 mm.
 5. A method as defined in claim 3, furthercomprising the step of removing the insulation of the phase conductorover a length of approximately 5-50 mm.
 6. A method as defined in claim3 for completing the connector for an aluminium cable further comprisingthe step of removing oxide from inner surfaces of the phase conductorsby applying contact grease.
 7. The method as defined in claim 3, furthercomprising the step of removing the insulation of the earth conductorover a length of approximately 90 mm.
 8. The method as defined in claim3, further comprising the step of removing the insulation of the phaseconductor over a length of approximately 20 mm.